(1) Field of the Invention
The present invention relates to a semiconductor device and a method for fabricating the same, and particularly to a semiconductor device adapted to incorporate a semiconductor element having a high heat release value thereinto and a method for fabricating the same.
(2) Description of Related Art
With expansion in functionality and reduction in size and thickness of electronic equipment in recent years, there has been a demand for thinner semiconductor devices. Thus, thin semiconductor devices with excellent heat dissipation ability and moisture-barrier properties have been developed. For example, Japanese Unexamined Patent Publication No. 2000-196006 discloses a semiconductor device having the structure that will be described below.
FIG. 22 is a plan view showing a semiconductor device 500 disclosed in the above publication. FIG. 23 is a cross-sectional view showing the semiconductor device 500 in FIG. 22.
As shown in FIG. 22, the known semiconductor device 500 comprises a die pad 51, a square semiconductor element 52 mounted on the die pad 51, four suspension leads (suspension members) 53, 53, . . . formed continuously with the die pad 51 and extending from the die pad 51 to the outside, a plurality of inner leads 54b, 54b, . . . provided between adjacent two of the suspension leads 53 and each having one end opposed to the corresponding edge of the semiconductor element 52, outer leads 54c, 54c, . . . formed integrally with the respective inner leads 54b and protruding toward the outside, a plurality of thin metal wires (thin conductive wires) 55, 55, . . . through which the semiconductor element 52 is connected to the inner leads 54b, and an encapsulation resin 56 for encapsulating therein the die pad 51, the semiconductor element 52, the suspension leads 53, the inner leads 54b, and the thin metal wires 55. In this relation, the die pad 51, the suspension leads 53, the inner leads 54b, and the outer leads 54c are formed of a conductive material, and the semiconductor element 52 is fixed on the surface 51a of the die pad 51 on which the semiconductor element is mounted (hereinafter, referred to as “semiconductor element mounting surface 51a”) by using a conductive adhesive 57. A desired voltage can be applied to the semiconductor element 52 by applying an external voltage to each outer lead 54c, leading to an available semiconductor device.
The die pad 51 has, outside its region on which the semiconductor element 52 is mounted, four wings 51b bent from the four edges of this region, respectively, toward the ends of the inner leads 54b. Therefore, the semiconductor device 500 has excellent moisture-barrier properties. Furthermore, as shown in FIG. 23, the surface 51d of the die pad 51 opposite to the semiconductor element mounting surface 51a (hereinafter, referred to as “exposed surface 51d”) is exposed from the encapsulation resin 56. Hence, heat generated in the semiconductor device 500 is dissipated through the exposed surface 51d to the outside. Thus, the semiconductor device 500 has excellent heat dissipation ability. In short, the semiconductor device 500 has excellent heat dissipation ability and moisture-barrier properties.
In order to fabricate such a semiconductor device 500, a conductive plate material is first processed to integrally form the above-described die pad 51, four suspension leads 53, 53, . . . , plurality of inner leads 54b, 54b, . . . , plurality of outer leads 54c, 54c, . . . , and plurality of thin metal wires 55, 55, . . . . The semiconductor element 52 is mounted on the die pad 51 and fixed thereon using the conductive adhesive 57. Then, the semiconductor element 52 is connected through the thin metal wires 55, 55, . . . to the leads 54, respectively. The die pad 51, the semiconductor element 52, the suspension leads 53, the inner leads 54b, and the thin metal wires 55 are encapsulated in the encapsulation resin 56. Thereafter, the outer leads 54c are shaped, thereby fabricating the semiconductor device 500 shown in FIG. 22.
When a semiconductor device is used for a pressure-resistant Plasma Display Panel (PDP) driver, motor driver or the like, the surface of a semiconductor element opposed to a semiconductor element mounting surface (hereinafter, referred to as “to-be-mounted surface of the semiconductor element”) must be grounded. The reason for this is that, in some diffusion processes for a semiconductor device, device characteristics vary depending on the potential of a substrate (the to-be-mounted surface of the semiconductor element) and in this case the grounding of the supporting substrate is essential for diffusion processes employed for the above-described drivers. However, the structure of the semiconductor device 500 does not allow the to-be-mounted surface of the semiconductor element to be grounded. This makes it difficult to use the semiconductor device 500 for PDP drivers, motor drivers or the like.
On the other hand, Japanese Unexamined Patent Publication No. 11-168169 discloses the structure of a semiconductor device in which the to-be-mounted surface of a semiconductor element can be grounded. As shown in FIGS. 24 and 25, a semiconductor device 600 disclosed in Japanese Unexamined Patent Publication No. 11-168169 comprises a tub (die pad) 61, a quadrilateral semiconductor chip (semiconductor element) 62 mounted on the tub 61, a plurality of tub suspending leads (suspension members) 63, 63, . . . formed continuously with the tub 61 and extending from the tub 61 to the outside, a plurality of inner leads 64b, 64b, . . . provided between adjacent two of the tub suspending leads 63 and each having one end opposed to the corresponding edge of the semiconductor chip 62, unshown outer leads formed integrally with the inner leads 64b, respectively, and protruding toward the outside, a ground connecting part 68 through which adjacent two of the tub suspending leads 63 are connected to each other and which is located between the semiconductor chip 62 and the end of each inner lead 64b opposed to the corresponding edge of the semiconductor chip 62, a plurality of bonding wires (thin conductive wires) 65, 65, . . . through which surface electrodes 65a located on the semiconductor chip 62 are connected to the inner leads 64b, respectively, and an encapsulant 66 for encapsulating therein the tub 61, the semiconductor chip 62, the tub suspending leads 63, the inner leads 64b, and the bonding wires 65.
The ground connecting part 68 is connected through another bonding wires 65, 65, . . . to the respective surface electrodes 65b, 65b, . . . located on the semiconductor chip 62 and through still another bonding wires 65, 65, . . . to respective inner leads 64b′, 64b′, . . . for grounding. Thus, the semiconductor chip 62 is electrically connected through the surface electrodes 65b, the bonding wires 65 and the ground connecting part 68 to the inner leads 64b′, 64b′, . . . for grounding. Therefore, the semiconductor chip 62 can be grounded by grounding the inner leads 64b′ for grounding.
However, a very small thickness of each bonding wire 65 might cause each bonding wire 65 to be cut during the fabrication of a semiconductor device 600. The semiconductor chip 62 and the ground connecting part 68 are connected through some of the bonding wires 65 to each other, and the ground connecting part 68 and each inner lead 64b′ for grounding are connected through one of the bonding wires 65 to each other. The cutting of the bonding wires 65 causes that the semiconductor chip 62 and the inner leads 64b′ for grounding are electrically disconnected from each other. As a result, the semiconductor chip 62 cannot be grounded. Therefore, utmost caution must be exercised in fabricating a semiconductor device 600, resulting in the extremely reduced production yield of semiconductor devices 600. Furthermore, new problems are caused. More particularly, since as shown in FIG. 25 the tub 61 is not exposed from the encapsulant 66, the semiconductor device 600 lacks heat dissipation ability. Since as shown in FIG. 25 the tub 61 does not have wings, the semiconductor device 600 lacks moisture-barrier properties.